Set of 0.5–0.9 mm carbide drill bits, a quick look at

As a brief digression, I’ll say that, strictly speaking, you can drill circuit boards with even a sharpened nail or needle. In fact, I’ve had to do that myself. It’s not very convenient, of course, but it’s entirely possible. I soon switched to regular small drill bits, although I did try using carbide ones too. More on that later; for now, let’s get to the review.

The store offers the drill bits in sets.
1. 0.5+0.6+0.7+0.8+0.9mm - link
2. 0.25+0.3+0.35+0.4+0.45mm - link

I chose the first option, since those sizes are the ones I use most often.

The drill bits come in a fairly handy little box.


The lid is attached with something like hinges. It opens and closes quite stiffly, at least while it’s new.
I’m used to storing drill bits in less convenient but more compact ways, so this setup felt a little unusual to me, but I liked it :)


The set contains 50 drill bits, 10 of each diameter.



Each drill bit is identified by a plastic stop ring of a particular color.
Purple - 0.9mm
Orange - 0.8mm
White - 0.7mm
Light blue - 0.6mm
Brown - 0.5mm


As I mentioned above, the drill bits are color coded by pants marked, but each one also has its diameter printed on it. For some reason, though, the markings vary slightly between bits.


One advantage of drill bits like these, as with end mills, is that they have a standard shank diameter, so you can use a collet or chuck of the corresponding size.
In this case, the shank diameter is specified as 3.175mm, probably one of the most popular sizes for small CNC machines.

My measurement came out at 3.17, but I used calipers, and they simply don’t have enough resolution (or accuracy) for this kind of measurement.
The cutting diameters are slightly undersized, by just 0.03mm, and they’re all off by the same amount in the same direction. So I can’t tell whether this is a measurement error or intentional; I’m inclined to think it’s the latter.
In practice, this is absolutely not critical, since runout will account for those 0.02–0.03mm anyway when drilling.


The lengths, on the other hand, vary noticeably. Here I’ve shown the two extremes; the other drill bits fall somewhere in between.
I hadn’t used drill bits with plastic markers before, but for some reason I thought they were necessary as stops, so the bit would always be set to a fixed drilling depth.


Here are a few more detailed photos of the drill bits and their cutting edges.
First, the largest diameter: 0.9mm.


The sharpening is quite good, although it’s a little different from what I’m used to.


Now the smallest one, 0.5mm.


There’s a small chip on one of the cutting edges, but it’s not a big deal in this case. I didn’t pick out specific bits for the photos; I just grabbed the first ones I came across at the two extreme diameters.


The sharpening is even—or, more precisely, symmetrical—which is very important. Poor sharpening not only increases the chance of breaking the bit (in this case), but if it doesn’t break, it can also produce an oversized hole.
I checked all the drill bits, and they’re all sharpened symmetrically and consistently.
The photo shows a 0.5mm drill bit.


I use regular drill bits, but a long time ago I bought ten domestically made carbide bits to try out. The first difference is the shank diameter: it’s smaller than on the ones reviewed here.


But every time I tried using these bits, they broke after just a dozen or so holes. A regular drill bit only breaks under heavy loads, while a carbide one is much more brittle—that’s the trade-off for greater hardness and a longer service life.
That’s why these bits aren’t suitable for handheld drills; you can see the result in this photo :(
No matter how firmly you hold a micro drill, runout and tilting are inevitable, so regular drill bits are the way to go for this kind of use.


A closer look revealed another fairly important difference. Domestic drill bits have what is called a “margin.”


You can see it in this drawing. The margin makes cutting easier and reduces the load on the drill bit, since the bit does not rub its entire surface against the material being drilled.


This same margin is also present on larger drill bits, so the bits under review are somewhat “simplified.” Domestic bits are essentially scaled-down copies of larger ones.


The cutting geometry on domestic bits is simpler than on the ones under review. The chisel edge (where the cutting lips meet) is wider than on the Chinese bits, so these bits will bite into the material and center themselves less effectively.


A photo of a broken domestic drill bit, added just for “company,” since I was looking at it under the microscope anyway :)


Since a handheld micro drill wasn't an option, all the tests were done on a small CNC machine.
To prepare the drilling program, I used StepCam_v1.78. First, I made a simple example in Sprint Layout, then exported it in Excellon format, opened the file in StepCam, and finally sent it to the software that controls the engraver.

At first, I played it safe and set the feed rate to 50 mm/min, but for the second part of the test I used 100 mm/min. I think the speed could actually be increased even further.


When I was getting ready to drill, I was worried about problems centering the bit in the chuck, and that runout in the chuck or machine itself might break the bits.
But I was genuinely surprised that none of the five bits needed any centering at all. I just inserted the bit, tightened the screws, checked that it was centered properly, and started the program. So I can say these bits are excellent in that respect.

But I ran into a problem that had nothing to do with the drill bits and everything to do with the process itself.
I created one file with all the required diameters and generated a program for the engraver's control software. But when it was time to change the bit diameter, the machine simply stopped, and there was nothing else I could do. I had to run each test separately using the same file.


Test results: I used 1.5 mm-thick single-sided FR-4, drilling from the copper side.
The top side looks pretty good, with a slight raised edge around the hole. This is probably due to the lack of a margin, and I don't think it's a major issue.


The underside looks a little worse; the bit doesn't exit cleanly, especially at 0.9 mm.


But I figured out the problem almost immediately: the plunge depth was too shallow at 1.9 mm, and the first test also started with the bit lifting quite high.
You can see in the photo that the top row of holes was drilled “right on the edge”; I should have let the bit go at least another 0.2-0.3 mm deeper.


For the second stage, I started drilling 210 holes at 0.7 mm, the most commonly used diameter.
After a relatively short time, it was already impossible to tell which hole was being drilled or how many were left. The software changes the drilling order based on the order in which holes were added to the PCB, rather than following the shortest path.
Drilling all 210 holes took about 11 minutes.


While drilling, I couldn't help remembering an urgent order that required me not only to route a PCB, but also to quickly make 10 devices at home.
I drilled them by hand with ordinary bits, reaching a speed of one hole per second. For comparison, the engraver drilled one hole every 3 seconds.
This is what that PCB looked like. The high speed was partly due to the large number of ICs.


The drilling went absolutely smoothly. Of course, a couple hundred holes is very little for testing a carbide drill bit; I should have run ten times as many.


Here I set a slightly greater plunge depth, but the exit still isn't very clean.


Although the bit reached the backing layer with room to spare. With manual drilling and a regular, but new, drill bit, the holes came out nicer, which is a little strange.


Unfortunately, I forgot to take a photo of the drill bit before the test, so I can only compare an unused bit with the one I used to drill a total of 236 (210+26) holes.
The test subject


The new one.
To my eye, there isn't much difference.


And now for a brief summary.
Advantages
Excellent centering
Good sharpening
No runout
The most common diameters are included in the set
Convenient storage case.

Disadvantages
No "ribbon"
Different lengths.
The exit side is a little "messy"

My take. I didn't analyze the material, but I can tell from the sound of the drill bit alone that it's clearly harder than ordinary bits. I'm pleased with the symmetrical sharpening and the almost complete lack of runout. In the review, I mentioned that I changed bits without making any adjustments. I was a little disappointed by the not-quite-clean hole on the exit side. It's hard to say what caused it; perhaps someone more knowledgeable can offer a suggestion.

And while solving one problem, I ended up with two more.
1. How do I get the software to "understand" when it's time to change the drill bit—or, more precisely, how do I get it to keep working? The software doesn't even turn off the motor, though it's supposed to raise the spindle for a bit change and turn off the motor.
2. What's the best way to drill a finished circuit board so the holes line up with their intended positions? I make boards using the toner transfer method, so larger boards can have a slight scaling shift. Is it better to adjust the "source file" or calibrate the machine?

The store provided a coupon for the review: HXFHG24. With it, the set costs 9.59. The coupon applies to both sets, links to which are at the beginning. As far as I understand, shipping is free.

That's all for now. As always, I'm looking forward to your questions—or, in this case, probably your advice :)